1. Field of the Invention
The present invention is generally related to snorkels used by skin divers. More particularly, this invention is related to devices for purging water from a snorkel.
2. Description of the Prior Art
Skin divers use the snorkel as a means to breathe while swimming face down on the water surface. The snorkel functions as a conduit between the diver's mouth and the overhead air (hereinafter "skin diver" and "diver" will be used interchangeably). Typically, when in use, the open end of the snorkel conduit extends a short distance above the diver's head. Occasionally, due to swimming movements or wave action, small amounts of water flow into the open end of the snorkel and partially flood the conduit. Also, water will flood the snorkel when the diver swims or dives below the water surface. An experienced skin diver can sense when water enters the snorkel and responds by immediately stopping inhalation. Respiration is resumed after the snorkel has been purged of water.
Inexperienced skin divers find occasional flooding especially troublesome because, undetected, water can be inhaled resulting in coughing and extreme discomfort. Consequently, several designs have been proposed to restrict or block the normally open end of the snorkel and thereby prevent water from entering.
U.S. Pat. No. 4,071,024 entitled Snorkel, issued to Max A. Blanc on Jan. 31, 1978, teaches an air entrapping cap which is mounted on the above water opening of the snorkel. A tortuous passage in the cap retards water flow into the snorkel. Although such a cap is somewhat effective in blocking the occasional flow of surface water into the snorkel, it also retards expulsion of water which enters the snorkel during a dive or swim below the water surface. The significant increase in respiratory and purging effort limits its utility and popularity.
U.S. Pat. No. 2,317,236 entitled Breathing Apparatus for Swimmers, issued to C. H. Wilen, et al, on Apr. 20, 1943, teaches a valve with a buoyant ball arranged to block the above water end of the snorkel whenever water starts to enter. Such valves are bulky, often fail to seal and, also, significantly interfere with respiration. Although once popular, such devices are now considered unreliable and obsolete.
The open snorkel conduit will be completely flooded with water when a skin diver returns to the surface after swimming or diving underwater. The open end of the snorkel is above the water surface when the skin diver assumes the face down, surface swimming attitude. With the open end of the snorkel above the water surface, the conduit is purged for respiration by exhaling an explosive blast of air into the mouthpiece.
Surface tension forms the purging blast of air into a bubble which spans the cross section of the conduit. Pressure within the bubble expands the bubble toward the open end of the snorkel conduit. As the leading surface of the bubble moves away from the mouthpiece, the bulk of the water within the conduit is pushed ahead of the bubble and out the open end.
The purging bubble of air will slip past water which adheres to the inside surface of the conduit. In general, little water will remain on the conduit's inside surface when the driving pressure within the bubble is substantially higher than ambient. Consequently, the purging bubble of air will slip past significant amounts of water only in the upper third of the conduit because the purging pressure of the explosively exhaled air is rapidly dissipated by distance from the mouthpiece.
After the purging air bubble is spent, residual water will flow down the inside surface toward the mouthpiece. Also, water which splashes into the open end of the snorkel conduit due to swimming movements or wave action will typically strike and adhere to the inside surface of the upper third of the conduit and thereafter flow down the surface toward the mouthpiece. Water accumulates at the lowermost portion of the snorkel conduit, typically under the mouthpiece, and obstructs the conduit. If the conduit is not completely blocked, a slow and cautious inhalation is possible after which another purging exhalation can be made.
The respiratory effort needed to purge a snorkel is significant. Many skin divers lack the respiratory strength needed to completely purge the snorkel with a single exhalation, and must repeat the purging procedure several times. Also, water will sometimes enter the snorkel just as the diver has completed an exhalation, leaving very little air in the lungs to satisfactorily complete a purge. Consequently, a means which decreases the respiratory effort and the amount of air required to purge a snorkel will be very beneficial.
A popular solution places an externally directed purge valve in the snorkel conduit at a location near the snorkel mouthpiece. Water in a flooded conduit which extends above the ambient water surface will drain through a purge valve. In other words, a purge valve drains the snorkel conduit until the water level within the conduit matches the ambient water level. Theoretically, because the total volume of water in the flooded snorkel is reduced by the initial flow through the purge valve, the respiratory effort required to purge the remaining water is also reduced.
Unfortunately, a purge valve also provides an alternate path for forcefully exhaled air. A purge valve will quickly and wastefully dissipate the explosive blast of purging air when the purge valve is located close to the mouthpiece. One solution to this problem places a purge valve in the snorkel conduit at a location approximately midway between the mouthpiece and the open end of the snorkel conduit.
At mid-length of the snorkel conduit, the purge valve will be close to the ambient water surface when the skin diver is swimming face down on the water surface. At such a location, the purge valve will drain that portion of the snorkel conduit which extends above the purge valve and the water surface, but will not initially interfere with the purging blast of air. Even at this location, the purge valve will dissipate the forcefully exhaled air and the amount of residual water adhering to the inside surface of the conduit between the purge valve and the open end will be substantial. Residual water subsequently accumulates at the lowermost portion of the snorkel conduit and obstructs the conduit. Consequently, a purge valve by itself, even when located mid-length of the snorkel conduit, is of limited benefit.
U.S. Pat. No. 4,278,080 entitled Diving Snorkel, issued to Joseph N. Schuch on July 14, 1981, teaches a purge valve located at the bottom of a branch conduit which joins the snorkel conduit at a location approximately midway between the mouthpiece and the open end. The purge valve drains the snorkel conduit until the water level within the conduit matches the ambient water level. Part of the purging air will divert into the branch conduit and force water within the branch conduit out the purge valve. Schuch teaches that the branch conduit must have sufficient length to provide the transient resistance necessary to allow purging of the snorkel conduit before the purging air reaches and is dissipated by the purge valve.
Water within the snorkel conduit of Schuch is pushed out the open end before the purging air clears the branch conduit of water and reaches the purge valve. Nevertheless, diverting part of the purging bubble of air into a branch conduit abates the driving pressure within the purging bubble and allows significant residual water to adhere to the upper portion of the snorkel conduit. Consequently, although the snorkel configuration of Schuch somewhat reduces the effort required to purge a flooded snorkel, it does not decrease the amount of purging air required, and it does not reduce residual water which adheres to the snorkel's inside surface and soon flows down the conduit to obstruct the snorkel near the mouthpiece. Also, the branch conduit adds significantly to the size of the snorkel, making the snorkel unwieldy in use.